Subterranean termites create tunnels with ascending and descending slopes under the ground for foraging. In this study, I explored the effect of the tunnel slopes on the termite ment, which is helpful in understanding the foraging efficiency. To do so, I designed five-cm long artificial tunnels in arenas. The tunnels had different curvatures (D) and widths (W). To artificially make the slopes, I obliquely put the arena with an angle, A(= 20°, 40°, and 60°). I systematically investigated the slope effect in terms of the time required for a termite to pass half the distance of the tunnel (τu for the ascending section and τd for the descending section). When A = 20°, little effect of the slope was observed, while for A = 40°, the slope effect strongly appeared. On the other hand, for A = 60°, the slope effect disappeared, which was explained by the ment behaviour. The results showed that an appropriate slope of ascending and descending tunnel could positively contribute to the termite ment efficiency.